# ---
# title: 1557. Minimum Number of Vertices to Reach All Nodes
# id: problem1557
# author: Indigo
# date: 2021-01-22
# difficulty: Medium
# categories: Graph
# link: <https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes/description/>
# hidden: true
# ---
# 
# Given a **  directed acyclic graph**, with `n` vertices numbered from `0` to
# `n-1`, and an array `edges` where `edges[i] = [fromi, toi]` represents a
# directed edge from node `fromi` to node `toi`.
# 
# Find _the smallest set of vertices from which all nodes in the graph are
# reachable_. It's guaranteed that a unique solution exists.
# 
# Notice that you can return the vertices in any order.
# 
# 
# 
# **Example 1:**
# 
# ![](https://assets.leetcode.com/uploads/2020/07/07/untitled22.png)
# 
#     
#     
#     Input: n = 6, edges = [[0,1],[0,2],[2,5],[3,4],[4,2]]
#     Output: [0,3]
#     Explanation: It's not possible to reach all the nodes from a single vertex. From 0 we can reach [0,1,2,5]. From 3 we can reach [3,4,2,5]. So we output [0,3].
# 
# **Example 2:**
# 
# ![](https://assets.leetcode.com/uploads/2020/07/07/untitled.png)
# 
#     
#     
#     Input: n = 5, edges = [[0,1],[2,1],[3,1],[1,4],[2,4]]
#     Output: [0,2,3]
#     Explanation: Notice that vertices 0, 3 and 2 are not reachable from any other node, so we must include them. Also any of these vertices can reach nodes 1 and 4.
#     
# 
# 
# 
# **Constraints:**
# 
#   * `2 <= n <= 10^5`
#   * `1 <= edges.length <= min(10^5, n * (n - 1) / 2)`
#   * `edges[i].length == 2`
#   * `0 <= fromi, toi < n`
#   * All pairs `(fromi, toi)` are distinct.
# 
# 
## @lc code=start
using LeetCode

function find_smallest_set_of_vertices(n::Int, edges::Vector{Vector{Int}})::Vector{Int}
    set = Set(edge[2] for edge in edges)
    res = Int[]
    for i in 0:n-1
        (i in set) || push!(res, i)
    end
    res    
end
## @lc code=end
